Next-generation SST faces ‘green’ barrier

It is almost five years since the Concorde retired, but little has been achieved in terms of replacing the world’s most iconic commercial aircraft. In 1994 the aim of the European Supersonic Research Project (ESRP) was a second-generation supersonic transport (SST) by 2010 (Mach 2, 250-seat, 5,500-nm range), but in the end, no program was launched and as the Concorde struggled to recover from the 2003 accident in Paris, the days of supersonic day trips from London to New York were numbered.

With environmental issues now at the forefront, few have dared to speak of “Son of Concorde” despite many expressions of dismay at progress seemingly going into reverse. Then there is the U.S. ban on supersonic flight over land, forming a formidable barrier even though International Civil Aviation Organization rules technically allow supersonic flight if there is no boom.

In fact, as Boeing found with its Sonic Cruiser experience, there is a vast array of technologies that need to be matured before a successor to the Concorde can enter service. As Kostya Zolotusky, Boeing’s managing director for capital markets development, told AIN, “Supersonic aircraft and the environment are not compatible. There’s been a fundamental shift on Boeing’s view, which switched when we dropped the Sonic Cruiser. Speed has an extraordinary cost in CO2 and fuel burn.”

Supersonic BizjetNevertheless, there is a growing consensus in the “supersonic community” that the sensible next step is to start with a supersonic business jet because there is a market for such aircraft and because it will allow many of the enabling technologies to be tested on a manageable scale.

Gulfstream has been working alongside NASA to develop enabling technologies–such as the “Quiet Spike” telescopic nose, tested by NASA Dryden on an F-15B in late 2006. “Essentially our position has not changed over the past three years,” said Robert Baugniet, Gulfstream director of corporate communications. “We do not believe there is a sound business case to be made for a supersonic business jet unless the regulations prohibiting supersonic flight over land are changed. To achieve this end we are conducting continuing research in sonic boom suppression with our patented extendable Quiet Spike and in close collaboration with NASA, and we also continue to do research in other areas including engine noise, use of composites and so forth.”

NASA’s vision is that with supersonic bizjets likely to enter service by 2015, this could be followed by a small airliner by 2020 (a 35- to 70-seat, Mach 1.6 to 1.8) and an “efficient multi-Mach aircraft” by 2030 to 2035. All three would be low sonic boom, supersonic over land and 30 percent more efficient than the Concorde.

“The principal focus of our current research is the generation that will follow the business jet– the small supersonic airliner, or the ‘N+2’ generation,” said Peter Coen, principal investigator for NASA’s Supersonics project. “We envision this vehicle to be similar in payload to the Concorde, but smaller and more efficient. More importantly, these aircraft will be green, in that they will meet the envisioned noise regulations and will have very low emissions.”

“One of the highlights of our current research is to try to reduce the sonic boom of such aircraft to the point where overland supersonic flight would be possible. This would be required to make these vehicles viable,” he added.

Coen explained that NASA’s Quiet Spike is a feature of a reference design, which also has top-mounted engines for noise shielding and variable geometry wings for low-speed performance. “This is meant to be an icon for the project and represents the potential contributions from all the areas of our project.”

NASA is also looking even further ahead. “We are considering what it would take to increase the utility and accessibility of supersonic flight in the 2030 time frame. Our ‘N+3’ vehicle studies will help us understand what this generation of vehicle might look like and what technologies would be required to make it viable,” explained Coen.Other enabling technologies that are part of NASA’s Fundamental Aeronautics Supersonics Project include cruise efficiency (for example, drag reduction, morphing geometry), airport noise considerations (noise reduction devices and optimum engine/airframe integration), aero- propulso-servo-elastocity (flutter, gust and maneuver load alleviation), lightweight structure and lowering emissions (using low-emission combustors and flight profiles).

Start-upsToday there are two leading contenders in the SSBJ race. One is Aerion, a company based in Reno, Nevada, that was formed in 2002 following work on supersonic laminar flow wings under DARPA’s Quiet Supersonic Platform program; the other is SAI (Supersonic Aerospace International), founded by CEO Michael Paulson in 2000 to fulfill the vision of his father, former Gulfstream CEO Allen Paulson, to achieve quiet supersonic flight. Both Aerion and SAI are seeking OEMs to take their proposed aircraft to market.

Aerion chief operating officer Mike Henderson, who headed Boeing’s high-speed civil transport (HSCT) program in the 1990s, told AIN that the Reno, Nevada-based company is taking refundable deposits of $250,000 on the $80 million purchase price and has been very successful, raising in excess of $3 billion. “People are looking for speed,” said Henderson. “Going to Mach 1.6 is a quantum leap… forty percent faster than a [Gulfstream] G650 and with a longer range than the Concorde.”

In fact, the aircraft will have a longer range subsonic than supersonic–4,600 nm at Mach 0.95 compared with 4,200 nm at Mach 1.45–and has a 120-knot approach speed thanks to its straight wing. Fuel burn at Mach 1.45 will be only 20 percent more than a G650 flying at M0.9, Henderson claimed.

“We’re talking to manufacturers and those interested have a draft schedule. Any one of the OEMs could do it,” he said. “The development cost would be around $2.7 billion, excluding the engine.” The engine in question will be the Pratt & Whitney JT8D, which should help it reach envisioned capacity of 2,000 hours a year.

The plan is to certify the aircraft in the first half of 2013. “The laminar-flow wing is a breakthrough along with the improved cruise so we can compete with [conventional] subsonic aircraft,” said Richard Tracy, chief technology officer of Aerion, told AIN.

SAI’s Paulson said last year that the QSST design was essentially complete but that it was looking for partners. The company contracted the Lockheed Martin Skunkworks to design the aircraft, which is planned to have a sonic signature one hundredth the intensity of the Concorde, partly thanks to a patented inverted-V tail.

London-based Wingman Consultants, which has compared the SAI and Aerion designs, concluded: “The Aerion is the strongest competitor, demonstrating a significant speed advantage over subsonic jets but at low technical risk and minimal increase in operating cost. Given that it can save three hours flight time on transatlantic routes from Europe, it can be said that the small increase in operating costs would be a worthwhile tradeoff for the potential revenue created.

“The SAI QSST shows much promise, but the high costs and reliance on regulation change make it a more uncertain investment,” the independent analysts stated. “Given a change in regulation, however, the QSST could be a resounding success.”The change of regulation referred to is supersonic flight over land. Just as the Concorde, the QSST is very inefficient at subsonic speeds, whereas the Aerion is not and can slow down over land with little penalty.

Europe’s HISACIn Europe, HISAC is a current “environmentally friendly high-speed aircraft” project, funded by the European Union and led by Dassault Aviation, involving 37 partners from 13 countries. Its main declared objective is to establish the technical feasibility of an environmentally compliant supersonic small-size transport aircraft (S4TA) through a “multidisciplinary optimization” approach and focused technological improvements. The initial benchmark aircraft would carry eight to 16 passengers at up to Mach 1.8 over a range of 3,200 to 4,900 nm.

The project’s first objective is to meet environmental requirements, while its second objective is to “provide policymakers with a set of recommendations for future environmental regulations that could reasonably be met with an optimized S4TA.” A third objective is to “provide progress on critical elementary technologies,” with the overall plan being to provide a “roadmap [leading] to a future proof-of-concept.”

Japanese BoomIn Japan, the Japan Aerospace Exploration Agency is developing a small supersonic aircraft for 30 to 50 passengers. “At JAXA our goal is to develop environmentally friendly supersonic aircraft with reduced sonic booms and noise pollution,” said an agency spokesman.

“We are also planning to build a silent supersonic technology demonstrator to verify our noise reduction technology. For sonic-boom suppression, while the U.S. has achieved it for only the front part of the airplane, we target the entire body. By the mid-2010s, we hope to accomplish a technology that will drastically reduce sonic booms, and we hope to build viable supersonic aircraft by the 2020s.”

JAXA aviation program group director Dr. Takashi Ishikawa admitted that Japan is focusing on specific technologies so it can be part of what can only be an international effort. “If we don’t, Japan will likely not be invited to participate,” he said.

So with Japan, the U.S. and Europe working hard on developing the enabling technologies, it looks as if the will does exist to overcome the challenges to a Concorde successor. That demand for a business jet looks to be good will help, as it provides a vital steppingstone that could be on a small enough scale not to create too much opposition. There is little doubt, however, that a successor to the Concorde will have to incorporate very advanced technology, which will mean an international collaborative effort.